1. Field of the Invention
This invention pertains to a conductive substrate applicable to printing processes used for supporting the image recording layer in electrostatic recording paper, electrical discharge recording paper, photosensitive media used for electrophotography, and the other types of recording media.
2. Prior Art
Heretofore, conductive substrates are conventionally used for supporting the image recording layer in electrostatic recording material, photosensitive media used for electrophotography, and other types of recording media.
Electrostatic copying and printing methods which employ media incorporating a conductive substrate and devices which employ such methods have enjoyed widespread popularity, including facsimile devices, printing and reproduction devices for mechanical drawings, schematic diagrams, etc., devices for printing proofsheets for use in proofreading for newspapers and other publications, and devices for copying official documents and the like. Furthermore, in recent years, refinements in electrostatic copying and printing methods have made production of multicolor copies and prints possible, which have been put to use for diverse applications including the field of design in general, as well as for production of advertisement and promotional fliers, programs for plays, sporting events and the like, and various other applications.
As a consequence of the growing popularity of electrostatic printing and copying methods, there is an intense demand for a recording media applicable to such applications, which incorporates a conductive substrate comprising a conductive layer showing an electrical sheet resistivity thereof in the range of over 10.sup.8 ohm/.quadrature., preferably in the range of 10.sup.8 -10.sup.11 ohm/.quadrature. at low or high relative humidity.
In general, a conductive substrate includes a substrate layer with at least one surface having a conductive layer formed thereover. An additive for supplying conductivity to the conductive layer is selected from electronic conductive materials and ionic conductive materials, depended on a required value of surface resistant of the conductive layer, for example when it is in the range of an electronic conduction region i.e. 10.sup.6 ohm/.quadrature. and under, the additive can be selected from various kinds of electronic conductive materials, on the other hand, when it is in the range of an ionic conduction region i.e. over 10.sup.6 ohm/.quadrature., the additive can be selected from various kinds of ionic conductive materials. Therefore the ionic conductive materials are generally used for preparing the conductive substrate with over 10.sup.8 ohm/.quadrature., preferably within the range of 10.sup.8 -10.sup.11 ohm/.quadrature. of electrical sheet resistivity thereof. However, it is found to be unstable in high relative humidity because the ionic conductive materials have poor moisture resistant properties, for example a value of electrical sheet resistivity of the conductive substrate in low relative humidity becomes remarkably high compared with One measured in high relative humidity.
To solve this problem, it has been investigated to produce a conductive substrate having a conductive layer with over 10.sup.8 ohm/.quadrature. of electrical sheet resistivity thereof by incorporating electronic conductive materials. Furthermore it has been also investigated to produce a conductive substrate including a conductive layer by incorporating an expensive material such as antimony oxide or tin oxide to prepare recording media which demonstrate significant resistance to low or high relative humidity.
However, despite an ongoing effort to develop recording media applicable to changes in relative humidity, it has not as yet been possible to produce such media.